Method of operating electrolytic cells



Jgnr4, 1938. E. SORENSEN METHOD OF OPERTING ELEgJTROLYTIC CELLS -3Sheets-Sheet 1 Filed June 25, 1936 INVENTOR BY I ATTORNEYS Jan. 4, 193

- E. soR'ENsEN,

METHOD OF OPERATING ELECTROLYTIC CELLS Filed Jfine 2s, 1936 3 Shets-Shet2 1 I IKIA I r 1 I 1 w w I I I II I I MHW MHHH INVENTOR ATTORNEYS Jan.4, 1938.

E. SO RENSEN METHOD OF OPERATING ELECTROLYTIC CELLO Filed June 23, 1936,

. I INVENTOR 6 am 41144 ATTORNEYS Patented Jan. 4, 1938 I UNITED STATESPATENT. OFFICE MZETHOD OF OPERATING ELECTROLYTIC CELLS Einar Sorensen,Rumiord, Maine, assignor to Oxford Paper Company, a corporation of MaineApplication June 23, 1936, Serial No. 86,725

. V lClaim. This invention relates to electrolytic cells for producingchlorine and sodium hydroxide from of the brine;

brine of the type disclosed in my prior Patent #1,613,966, issuedJanuary 11, 1927, and more palil'ticularly to the method of operatingsuch a ce The cell disclosed in my priorpatent coinprises a casinghaving a longitudinal partition which divides the cell intoadecomposingcompartment and an oxidizing compartment. Brine, to betreated, enters the decomposing compartment, the floor of which iscovered with'a slowly moving layer of mercury which constitutes acathode. Graphite plates 1 located above the mercury constitute theanode. Electric current passing between the graphite plates and themercury liberates chlorine irom the brine and the mercury forms anamalgam with the sodium The amalgam flows out of the decomposingcompartment into the oxidizing com- 1 partment where it passes-overnotched graphite plates. Measured quantities of water are fed into theoxidizing compartment. By the action.

set upin the oxidizing compartment the amalga n is decomposed and thesodium reacts with the water to f rm sodium hydroxide solution.

The mercury t us freed of its sodium thenenters a pump chamber in whicha rotary pump liits the mercury and returns it to the decomposingcompartment.

In the operation of electrolytic cells of the kind described abovehydrogen gas is liberated during the reaction that takes place in theoxidizing compartment, The hydrogen gas escaping from the cell entrainssome of the caustic. This results in a small loss of caustic but a moreserious consequence is that the caustic entrained by the escapinghydrogen contaminates the cell room atmosphere.

The object of this invention is to provide a" method of operating a cellof the general type described above that will prevent the entrainment ofcaustic by the escaping hydrogen gas.

This is accomplished by providing-a liquid seal for the oxidizingcompartment by'maintaining on the body of caustic a floating layer of aliquid which will permit the hydrogen gas to escape through it but whichwill hold back any caustic which tries to escape with the hydrogen.

An electrolytic cell capable of being operated by my method is shown inthe accompanying drawings, but it is tobe understood that the method isapplicable to cellsdiifering very materially from the one illustrated.The particular cell shown'in the drawings is an improve ment on thecellshown in my priorlpatent above referred to and certain features notclaimed herein are claimed in my co-pendlng applications, Serial No.43,027, filed October 1, 1935, 'Serial NO. 81,344, filed May 23, 1936,Serial N0.

93,580, filed July 31, 1936 and Serial No. 97,884, iiled August 26,1936.

In the drawings: V

Figure 1 is a plan view of the cell with the cover and the anodeassembly of the decomposing compartment removed to expose to view theinterior. construction of this compartment;

Fig. 2 is a longitudinal section through the deof Fig. 1. In this Viewthe cover and the anode assembly are in place; I

Fig. 6 is a longitudinal section through the oxidizing compartment takenon the line 3--3 of Fig. 1; E

Fig. 4 isa detailed sectional view of one "end of the oxidizingcompartment taken on the line 4-4 of Fig.1;

Fig. 5 is a sectional view similar to Fig. 4 taken 7 on the line 5-5 ofFig. 1; g

Fig. 6 is a'transverse section taken on the line 6-6 of Fi 1; p

composing compartment taken on the line 2--2 Fig. 7 is a transversesectiontaken :Iust to the rear of the section of Fig. 6, i. e., on theline 1-4 of Fig. 1; i

Fig. 8 is a transverse section taken just to the rear of the section ofFig. 7, i. e., on the line 8-8 of Fi 1, and j Fig. 9 is a transversesection taken on the line 9-9 of Fig.1.

The cell illustrated in the drawings has an external metal casing lwhich is generally rectangular in shape as shown in Fig. 1. It isdivided into two compartments by a longitudinal partition 2. One ofthese compartments, designated 3, is the decomposing compartment and theother one designated 4 is the oxidizing compartment. As best shown inFigs. 6 to 9, inclusive, that part of the metal casing which houses theoxidizing compartment projects .downwardly to a lower-level passagethrough the channels 45, 46 and-"and is discharged through the passage 9into the ox-' idizing compartment. the mercury is indicated by thearrows in Fig. 1. The mercury'in the decomposing compartment io'rms thecathode of an electric circuit, the anode being graphite plates l0supported with their lower faces just above the-surface oi the mercury.As the mercury passes through the The directionof flow of tion tomaintain the desired depth of brine within the decomposing compartment.

In the oxidizing cell the mercury amalgam passes over the notchedgraphite plates l2. are fed into this scribed to maintain in thiscompartment a pre determined density and -to compensate for. the

water consumed in' the displacement action. The displacement'actionwhich takes place in this cell frees the amalgam of its sodium andcauses the sodium to unite with the water to form" sodium hydroxidesolution. The sodium] hydroxide solution is withdrawn from the oxidizingcompartment through a pipe I! (Figs. 1'

and 9) which discharges into the lower end of receptacle M. Thisreceptacle has a vertical partition l5 dividing it into twocompartments. The sodium hydroxide solution enters the bottom of theright hand compartment (as. viewed in'Fig. 1) and flowsover the upperedge of the partition It is then- IS into the left hand compartment.discharged through an outlet pipe I! in the bottom of the left handcompartment. In the right hand' compartmentthere may be located ahydrometer ll (Fig. 9) by which the density of the sodium hydroxidesolution may be measured. The level of the sodium hydroxide solution inthe oxidizing compartment is determined by the elevation of the upperedge of the partition l5.

Therefore, the level of the sodium hydroxide solution in the oxidizingcompartment may be varied. if desired, by raising or lowering thereceptacle i4 and thereby raising or lowering the elevation of the upperedge of the partition 15. This may be effected by providing the pipe IIwith a removable section I. which may be replaced by a longer or shortersection.

The mercury freed of its sodium passes into a pump well It. A rotarypump 20 lifts the mercury from the well and discharges it at a higherelevation where it flows into the passage 8 of the decomposingcompartment thereby completing the cycle. The pump has a series ofperipheral pockets 2| (Fig. 6) to which the mercury is admitted throughperipheral openings 22. It is discharged from these pockets throughopenings 23 (Figs. 7. and 8) in the lateral wall of the pump. It is thencaught in the manner herein: after to-be described and passed on to thedecomposing compartment. The mercury pump is operated by' a sprocketwheel 24 connected by means of'a chain 25 (Fig. 6) to -a sprocket wheel28 (Fig. 3) on a any suitable manner.

The water to be supplied to the oxidizing compartmentflrst enters areceptacle 28 through a pipe 20. A pipe Ill having an elbow 3| at itsouter end, which forms a small bucket, is oscillated so that it dipsdown into the water in the receptacle 28 and then as the pipe rises thewater flows through the pipe and is discharged from the inner end 32 ofthe pipe into another compartment 33 of-the receptacle 28. The pipe 30is mounted on a horizontal shaft 34 to the outer end of which isconnected an arm 85;. This arm is engaged and deflected by a projection35 associated with the sprocket wheel 24 so. that every Fig. 1)- thereis a drive shaft 21 driven in the compartment 88 the water passesthrough a pipe 811 directlyinto the pump well l9. The pump picks up boththe mercury and the water and the manner in which the water and mercuryare separated so that the water is delivered to oxidizing compartmentand the mercury delivered to the decomposing compartment will behereinafter described.

The anode plates II are rigidly fastened to, and suspended from, thecover 53 of the decomposing compartment and forms unit therewith. Eachanode plate is rigidly secured to the cover 53 by a graphite lead '1threaded at both ends. .The lower end of the lead I1 is screwed into theanode ll, as'shown at I! and the upper end of .the lead passes throughan opening in the cover 53 and is clamped to the cover by a fibre nut59. In the particular cell shown in the drawings there are three anodeplates in each channel thus making nine all together. The three anodeplates of each traverse row are electrically con- 7 bedded in theconcrete floor of the decomposing compartment are a series oftransversely extend ing metal bars or strips 83 (Figs. 1 and 2).

These are supplied with current by a bus bar 64. I

Bolt terminals a are screwed and welded to the transverse bars'flandextend through the metal container and are secured to the bus bar 64 bymeans of nuts 64b. Over each metal bar 63 the concrete floor is providedwith.a series of holes Giby means of which the mercury makes contact 7with the bar. The path of the current is therefore from the bus bar N tothe bolts 41, to the transverse bars 63, then to the mercury cathode,through the brine to the graphite anodes Ill, then .through the leads 51and connecting strips to the bus bars 62. After the mercury leaves thedecomposing compartment and before it enters the oxidizing com partmentit forms a seal and thereby prevents brine from passing from thedecomposing compartment to the-oxidizing compartment. This seal istherefore called the brine seal" and is constructed as follows: At theright hand end of the oxidimng compartment l (as viewed in pit or well10 molded in the concrete lining; In plan view this well is relativelynarrow longitudinally of the cell and is relatively long transversely ofthe cell. The bottom of the well is tapered to form a V as shown at H inFig. 9, the taper being ,in such a direction that the mercury passingfrom the decomposing compartment through the passage 0 will flow downone of the arms of the V'.

The well 10 forms one of the chambers ofthe brine seal,-the otherchambeig'shown at 72, (Figs.

1 and 3) being a pit located in the floor of the ening 13 extendingthrough the wall I4 that sep-.

arates the well 10 from the oxidizing compartment. It is obvious fromthis arrangement that a body of mercury will be maintained in thechambers 10 and 12 of the seal at a constant level. As the mercury iscontinuously fed into the well 10 it is ,continuously discharged fromthe pit 12 into the oxidizing compartment. The body of mercurymaintained in this manner by the seal "3,104,070 chambers and "I2prevents anybrine from'ening 13. The mercury thus passing into the welldizing compartment through the seal and may enwash water through the aThis prevents brine from being the mercury as it passes into theoxidizing compartment thus maintaining purity of the sodium hydroxidesolution produced in the oxidizing com- I0, down one side of thev-shaped bottom and partly up its other side has its velocity spent.entrained with Dartment. The well 10 also serves as a concentrationpoint for any broken up or dispersed mercury as well as any precipitatedgraphite from the anodes. This concentrated material can be easilyremoved during operation of the cell which greatly lengthens the time ofoperation possible between wash-ups. It is important to concentrate andremove the dispersed or broken up mercury for otherwise it will passinto the oxitrain some of the brinej Furthermore, any dispersed mercurywhich finds its way into the oxidizing compartment will remain insuspension in the sodium hydroxide solution and pass oil. with itthereby causing a continuous loss of mercury. The outer wall of the well10 has anormally closed pipe 15 extending through it which communicateswith the interior of the well and affords a convenient outlet for thewash water during washups. Moreover, by discharging the I pipe 15 it isprevented from entering the oxidizing compartment.

In passing from the oxidizing compartment into the pump well, themercury forms a second seal called the caustic seal because it preventscaustic from passing along with the mercury to the pump well. a Thisseal comprises a pit 71 molded in the concrete floor of the oxidizingcompartment anda pit I8 molded in the concrete floor of the pump well(Figs. 3 and 5) Communication between these two pits is established by apassage 19 in the wall 80 which separates the oxidizing compartment.from the pump well. The body ofmercury maintained in the 'cham; bers andI8. at a constant level constitutes a seal similar to the one previouslydescribed. As the mercury is continuously fed into the compartment 11 itis continuously discharged from the compartment 18 into the well of themercury pump but no caustic can pass into the pump well.

28 picks up the mercuryin the pump well and also the water which hasbeen fed to the pump .well by the water bucket 3!, already described.

and 7), which conducts them to a third mercury seal called the waterseal because it prevents the water from passing alongwith the mercuryinto the decomposing compartment. This seal is formed by pits 82 and 83molded in the con-' crete and a connecting passage M which places thebottom of these pits in communication, (Figs. 1, 3, 4, 5, 6, and 7.). Asthe mercury is continui ovsly fed into the pit 62 it is continuouslydischarged over the edge 85 and then passes into the transverse passageB which conducts the mercury to the first channel 45' of the decomposingcompartment. The water held back by the seal 82-83-84 and which floatson top of the mercury as it passes through back into the pump well.

As previously stated the rotary mercury pump oi the pit 33 (Fig. 6)

splash of the mercury as it is discharged from the pump 20. Splashing ofthe mercury at this Point would be harmful as it would cause break-- ingup or dispersing of the mercury or would also augment vaporization.Prevention of vaporization of the mercury is very important from ahealth standpoint. A spill plate 81 (Figs. 1 and 3) extends from thebottom of the trough ll to I a point closely adjacent the dischargeoutlets 23 of the pump to prevent .spill of the mercury The water in thetrough ll (supplied by the oscillating bucket 31 to the pump well anddelivered by the pump to the trough 8|) acts as a. cushion for thefalling mercury. It also acts as a wash and a submerging cover for themercury the water seal 8243-84.

As previously described the oscillating water bucket]! supplies auniformand measured quantity of water to the oxidizingcompartment. As

during its travel to the water is first delivered to the pump well'itkeeps the mercury in the pump well and-in the pockets of the pumpcovered with water and thereby prevents vaporization of the mercury andthe consequentcontamination of the;room atmosphere.

In the oxidizlng compartment hydrogen gasp is liberated whenthe sodiumis freed from the amalgam and reacts with the water to form sodiumhydroxide solution; The hydrogen gas is v usually permitted to escape tothe cell room atmosphere and in so doing entrains a small amount ofcaustic. In order toprevent entrainment of caustic by the liberatedhydrogen gas I maintain on the body of caustic in the oxidizingcompartment a; liquid seal shown at 16 in Fig. 3.

The liquid floats on the surface of the caustic and permits the hydrogengas to bubble through it but holds back any caustic which wouldotherwisebe entrained by the escaping hydrogen gas.

Prevention of entrainment of caustic by the hydrogen gas which isliberated-to the cellv room atmosphere is ,an important considerationfrom a, health standpoint. It also decreases the loss of caustic.

It will be noted from the foregoing description tain' in the oxidizingcompartment a body or caustic solution having suilicint depth to preventthe liquid floating on its surface from contactingnwith the mercury onthe floor of the oxidizingcompartment. This is made clear in Fig. 3 ofthe drawings. the caustic in the oxidizing compartment can beadjusted'by varyingthe elevation of theupper edge of the partition I6 inthe caustic discharge re ceptacle l6.

The liquid employed for the seal lighter thanthe caustic solution sothat it will float upon it, and it should have suflicient fluidity toenable the hydrogen to escape through it. The material used forthellquid seal should preferably possess the following additionalcharacteristics; inertness with respect to the caustic, immiscibilityin'caustic andwater and inability to emulsify with either; a sumcientlyhigh boiling point to prevent excessive vaporization and freedom frommetallic impurities which would otherwisacontaminate the caustic and themercury. 'I have found that a hydrocarbon mineral As above stated thelevelof 4 gimme.

and have mcceaeoil 18 Mutable for the. fully used such an oil having thefollowing specincationsz Type or baae I claim:

The method of operating an eiectroiytic of the type which has ndecomposing commit-'- mient and an oxidizin: comportment throulh whichmercury may be circulated, which oomprises producin: and maintainin:lbod! 0! canstic solution in the oxidizin: compartment. and

maintaining on the surface of the caustic eolution a. layer'oi'hydrocarbonminenl oil which is inert with respect to the. amide andwhich has sumcient fluidity to permit :03 produced in the oxidizingcompartment .0 escape through it tvhereby the entrainment oi cauatic bythe eslocaning gas is prevented.

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